Aerosol products are well known in the art and have good consumer acceptance based on their ability to deliver a material to a surface in a convenient, hygienic manner. This benefit has made aerosols, the product form of choice for antiperspirants for many of the world's consumers. Aerosol antiperspirants deliver a fine spray of antiperspirant that can completely cover the axilla and provide a cool and dry sensation during application.
Typically aerosol antiperspirant products are in the form of a liquid or solid-in-liquid suspensions that are contained under pressure in a metal canister and delivered at a controlled flow rate via a sealing valve. The product is usually delivered by depressing an actuator or similar mechanism, which opens the valve, and then the pressured product is forced through the valve. Pressure is created in the canister by the inclusion of a gas or liquefied gas propellant in the product canister. The propellant can be an integral part of the product or simply create pressure in the headspace above the product. Common propellants include liquefied gases such as butane, isobutane, propane, dimethyl ether, and 1,1 difluoroethane.
These aerosol products (e.g., aerosol antiperspirants) can be highly flammable and can create a substantial fire hazard during storage. In a fire, aerosol canisters can rupture or BLEVE (boiling liquid expanding vapor explosion) and release flammable components such as propellant, hydrocarbons, alcohols, or other flammable compounds, which can then be ignited by the fire thus resulting in further spreading of the flames. Furthermore, some aerosols when exposed to fire have been known to rupture and “rocket with trailing burning liquid” away from their original position and spread the fire to previously unaffected areas. The fire hazard of an aerosol product is shown by its hazard category. Hazard categories of Level 1, 2, and 3 are based on the amount and type of flammable material in the product. More specifically, if a product has a chemical heat of combustion that is from 0 to 8,600 Btu/lb (20 kJ/g), then the product is classified as a Level 1. Similarly, if a product has a chemical heat of combustion that is from 8,600 Btu/lb (20 kJ/g) to 13,000 Btu/lb (30 kJ/g), then the product is classified as a Level 2. Lastly, if a product has a chemical heat of combustion that is greater than 13,000 Btu/lb (30 kJ/g), then the product is classified as a Level 3.
The fire hazard classification of an aerosol product is used to determine proper storage conditions. These storage conditions include necessary sprinkler design, storage height, and secondary container. Level 1 products have the least stringent storage conditions. Level 2 and 3 products have storage requirements that are more commensurate with their increased risk. Level 3, having the most risk, has the most stringent and expensive requirements. These stringent storage conditions increase the cost and the complexity of merchandizing aerosol products. Storage regulations are described in detail in “NFPA 30B Code for the Manufacture and Storage of Aerosol Products 1998 Edition”, and is hereby incorporated by reference.
Typically, aerosol products are contained in metal canisters made of aluminum or tin plate. These canisters have a good mechanical strength and heat resistance that significantly reduce the fire hazard by providing a substantial barrier between the flammable product and fire. Metal canisters are often capable of containing products with pressures as high as several hundred PSI so the temperature at which the canister fails and BLEVE occurs can be quite high. Moreover the metals that these canisters are composed of typically have melt temperatures that are greater than 400° C.; therefore, they are not subject to failure due to melting at relatively low fire temperatures (below 200° C.).
It has long been desirable to develop plastic packaging for aerosol products. Moving from metal to plastic provides several benefits such as increased freedom in developing unique canister shapes, developing clear packages, and lowering manufacturing costs. Unfortunately, these plastic packages have shown poor manufacturing and storage stability. Many of these packages are degraded by the product components resulting in package discoloration, swelling, loss of pressure, and in some extreme cases the packages burst during the filling process. Recent development of plastic materials with the necessary physical strength and chemical resistance has finally allowed the development of commercial plastic aerosol packages. Unfortunately, these recently-developed materials typically have a melt point or glass transition temperature less than 200° C.; therefore, it is possible for these packages to fail at lower temperatures than metal canisters and thereby create an increased fire hazard during warehousing as compared to metal canisters. The simplest route to reducing fire hazard is to include water in the product. In fact, the use of plastic packages is preferred when formulating with aqueous solution of antiperspirant active since metal packages often corrode when in contact with these solutions. Unfortunately, water is known to degrade some antiperspirant actives so often it is preferable to formulate anhydrous products.
Since current plastic packages provide a less substantial barrier between the flammable aerosol product and a fire as compared to metal canisters, it is desirable to formulate products for these plastic packages that have a reduced fire hazard classification of level 1 or 2 in order to reduce the overall fire hazard classification of the product package combination. This can be achieved by proper choice of propellant type and level, product solvent type and level, and amount and type of inert ingredient(s).
Typically, aerosol antiperspirants contain 30-85% of a hydrocarbon propellant and thus often have a fire hazard rating of 3. It is the intent of this invention to provide aerosol products that when formulated in stable plastic package provide a level 1 or level 2 fire hazard classifications.